Details

The chances of the spring mean maximum temperature exceeding the long-term median maximum temperature are greater than 60% over Tasmania, south-western Victoria and coastal fringe areas of South Australia (see map above). Such odds mean that for every ten years with similar climate patterns to those currently observed, about six to eight spring periods would be expected to be warmer than average over these areas, while about two to four years would be cooler.

Conversely, there is a 30 to 40% chance of warmer than normal days over southern New South Wales, northern and central Victoria and an area of southeast South Australia. In other words, there is a 60 to 70% chance of cooler than normal days in these areas.

The chance that the average minimum temperature for spring will exceed the long-term median minimum temperature is in excess of 60% across most of South Australia, parts of northern New South Wales and the east coast, and an area of southern Victoria. Probabilities exceed 80% right across Tasmania.

Over the rest of southeast Australia, there is no strong tendency towards warmer or cooler nights than average.

Climate influences

The negative Indian Ocean Dipole (IOD) event that has been influencing Australian climate since mid-May has weakened over the past four weeks. Despite this, sea surface temperature patterns continue to be consistent with a negative dipole event. The majority of climate models expect this negative IOD event to persist until mid-spring. A negative IOD during the winter-spring period increases the chances of above normal rainfall, and thus cloud amount over southern Australia. Increased cloudiness reduces sunshine hours and hence daytime temperatures over inland Australia.

The tropical Pacific has remained ENSO-neutral since mid-2012. The dynamical seasonal outlook model suggests ENSO-neutral conditions will remain for the rest of 2013. This means there is no strong shift in the odds from the tropical Pacific.

Warmer than normal sea surface temperatures currently surround much of southern Australia. Warmer sea surface temperatures will tend to influence air temperatures in those areas closer to the coast.

How accurate is the outlook?

Outlook accuracy is related to how consistently the oceans and broadscale climate affect
Australian temperatures. During September to November, historical accuracy shows the outlook for
maximum temperatures to be moderately consistent over most of southeast Australia.

The effect on minimum temperatures during this season is moderate over most of southeast Australia excluding the northeast coast of NSW, northwestern parts of Victoria and the southern tip of Tasmania where the effect is only weakly to very weakly consistent.